The present invention relates generally to hermetic compressors of the type including a motor-compressor unit disposed within a hermetically sealed housing having an oil sump in the bottom thereof. More particularly, the invention relates to apparatus for minimizing turbulence within the housing during compressor operation, thereby reducing undesirable agitation of oil in the oil sump.
A common design for a hermetic compressor is to have the electric drive motor in the bottom portion of the housing, adjacent the oil sump, and the compressor mechanism in the top portion of the housing. In such an arrangement, the crankshaft of the compressor mechanism ordinarily is coaxially disposed within the motor rotor and operably engaged thereby. A lower end of the crankshaft extends into the oil sump so that oil can be pumped therefrom, through a passageway in the crankshaft, to the compressor mechanism. The lower axial end of the motor rotor adjacent the oil sump will typically include an axially protruding, arc-shaped weight adapted to counterbalance eccentric rotating masses associated with the compressor mechanism at the opposite end of the crankshaft.
Prior hermetic compressors included cast counterweights in the rotor end rings having axial steps. These end rings provided the necessary rotor imbalance but agitated oil within the oil sump. Other compressors included counterweights with hollows or holes to provide smooth bottoms trying to prevent oil agitation, but these also had additional parts that added to the cost of the compressor. An example of such a compressor with a separate counterweight shield is shown in U.S. Pat. No. 5,064,356.
A problem arises in the aforementioned hermetic compressors having a rotor equipped with a counterbalance weight adjacent the oil sump, in that the rotating rotor causes turbulence within the housing, which agitates the oil in the oil sump and results in lower quality oil for lubrication purposes. Specifically, turbulence may either displace the oil in the sump so as to cause an interruption of oil being supplied to the bearings, or aerate the oil to a foamy condition. In either case, failure to provide a constant supply of high quality oil may result in damage to the bearings or in inability of the compressor to function properly. The problem is exaggerated in compressors employing centrifugal rather than differential pressure pumping, because the oil flow rates are lower and interruptions in the supply of high quality oil take longer to correct themselves.
It is known in the prior art to weld a cup to the bottom of the housing, into which the oil pick-up tube on the end of the crankshaft extends. In this manner, oil must first enter a quiet zone within the cup prior to being drawn into the pick-up tube. However, this has proven only marginally successful in eliminating the adverse effects of turbulence. Another prior art device involves a horizontal separating plate that is welded to the housing intermediate the oil sump and the drive motor. The oil pick-up tube extends through a hole in the plate in order to access the oil. This method has several disadvantages, including added material and increased manufacturing costs, the need to weld to the housing, and an increased axial dimension of the housing to accommodate the plate.
While prior art attempts to ensure high quality, placid oil in the oil sump of a hermetic compressor have been somewhat successful, it is desired to provide an improved apparatus for minimizing the turbulence within the compressor housing that is attributable to the motor rotor and counterbalance weight.